1. Technical Field of the Invention
The present invention relates to cellular telephone networks and, in particular, to the routing of telephone calls to and from mobile stations engaged in international roaming.
2. Description of Related Art
The mobility benefits provided to subscribers by cellular telephone networks comprise, perhaps, their most important and effective marketing advantage over and technical distinction with respect to conventional wire line telephone service. It is common for subscribers then to use their mobile stations not only in the immediate geographic areas surrounding their homes and businesses, but also to travel outside of their home cellular service area to other cellular service areas. When this occurs, the subscribers and their mobile stations are said to be "roaming".
Within one country, the plural cellular systems scattered throughout that country are generally technically compatible with each other. If the various service providers have billing and other reciprocity service agreements with each other, a cellular subscriber may then roam among and between those service areas and still make and receive telephone calls. The process of registering in the visited system occurs transparently to the subscriber. Even absent an agreement with respect to billing, the overall system technical compatibility allows the subscriber to arrange for a personal billing agreement with the service provider, and thus access the visited cellular system to make and receive telephone calls. With respect to the reception of calls, the subscriber mobile station is reached by dialing its originally (permanently) assigned directory number.
The number of people owning cellular mobile stations has dramatically increased in recent years. Furthermore, an increasing number of geographic locations now have access to a cellular telephone service. With this increase in numbers of users and service availability, there also exists an increasing number of instances where subscribers have the capability, and the desire to engage in, of cellular roaming. In fact, it is now common for persons to take their cellular mobile stations with them on business trips and vacations. Often times these trips and vacations involve travel to a different country.
While technical compatibility with the cellular system in the visited country may be present, it is unlikely that the service provider in the visited system and the subscriber's home service provider have agreed to service provision and billing arrangements with respect to internationally roaming subscribers. The subscriber must accordingly contact the service provider in the visited country and manually register their mobile station for service. Once registered, the subscriber may then make a cellular telephone call. Receiving a cellular telephone call, however, further requires the assignment by the service provider of a temporary directory number to the subscriber's mobile station. A party desiring to call the subscriber may then have to use the assigned temporary directory number rather than the subscriber's home directory number in placing an international call to the subscriber. Accordingly, to be accessible for incoming calls while engaging in international roaming, the subscriber must inform others of the newly assigned temporary number. Inconveniently, this number is valid only for the currently visited cellular system. If the subscriber should thereafter move to another country (or even switch service providers within a single country), or perhaps change to a different switch of the same service provider in the same country, another manual registration must be made and another temporary directory number is assigned for subsequent use.
There is a need then for a more efficient method and system for enabling subscribers to engage in international roaming. Preferably, such a method and system would allow a subscriber to maintain use of their home directory number.